The present invention relates to novel additives for coating compositions that provide improved mar and/or scratch resistance to cured coating compositions.
Coating systems can have many variations including xe2x80x9ccolor-plus-clearxe2x80x9d coating systems and xe2x80x9cmonocoatxe2x80x9d coating systems. Color-plus-clear coating systems involve the application of a colored or pigmented basecoat to a substrate followed by the application of a transparent clearcoat over the basecoat. Such coating systems have become increasingly popular as original finishes for a number of consumer products including, for example, cars and floor coverings such as wood flooring. The color-plus-clear coating systems have outstanding appearance properties such as gloss and distinctness of image due in large part to the clearcoat.
Monocoat coating systems involve the application of a single layer of colored coating to a substrate as the topcoat. Monocoat coating systems are frequently used for household appliances, lawn and garden equipment, interior fixtures, and the like.
Both color-plus-clear systems and monocoat coating systems can utilize powder coatings. In recent years, powder coatings have become increasingly popular because these coatings are inherently low in volatile organic content (VOC). The low VOC significantly reduces air emissions during application and curing as compared to liquid coatings. Liquid coatings are still used in many systems, however, particularly those wherein solvent emissions are permitted. For example, the coating of elastomeric automotive parts is often done by spraying liquid compositions.
Topcoat film-forming compositions, such as the protective and/or decorative one coats for household appliances and the transparent clearcoat in color-plus-clear coating systems for automotive applications, are subject to defects that occur during the assembly process and damage from both the environment and normal use of the end product. Paint defects that occur during assembly include the paint layer being too thick or too thin, xe2x80x9cfish eyesxe2x80x9d or craters, and under-cured or over-cured paint. These defects can affect the color, brittleness, solvent resistance and mar and scratch performance of the coating. Damaging environmental factors include acidic precipitation, exposure to ultraviolet radiation from sunlight, high relative humidity and high temperatures; these factors can also result in compromised performance. Normal use of consumer products will often lead to marring, scratching and/or chipping of the surface due to contact with hard objects, contact with brushes and/or abrasive cleansers during normal cleaning processes, and the like.
Thus, there is a need in the coatings art for topcoats having good scratch and mar resistance.
The present invention is directed to an additive for use in coating compositions, including both liquid and powder coating compositions. The additive generally comprises particles dispersed in at least one siloxane compound. Coating compositions comprising the additive and methods for using the same are also within the scope of the invention, as are articles coated according to these methods.
Historically, the incorporation of particles into coatings, especially powder coatings, has been very hard to achieve. It has now been surprisingly discovered that particles can be introduced into a coating composition using a siloxane compound; the siloxane compound acts as a carrier to introduce the particles into the coating composition. Coatings comprising the present additive have enhanced mar and/or scratch resistance as compared with the same coatings lacking the additive. According to the present invention, coatings can be formulated with improved mar and/or scratch characteristics without significantly affecting the appearance or other mechanical properties of the coatings.
xe2x80x9cMarxe2x80x9d and xe2x80x9cscratchxe2x80x9d refer herein to physical deformat ions resulting from mechanical or chemical abrasion. xe2x80x9cMar resistancexe2x80x9d is a measure of a material""s ability to resist appearance degradation caused by small scale mechanical stress. xe2x80x9cScratch resistancexe2x80x9d is the ability of a material to resist more severe damage that can lead to visible, deeper or wider trenches. Thus, scratches are generally regarded as being more severe than what is referred to in the art as mar, and the two are regarded in the art as being different. As noted above, marring and scratching can result from manufacturing and environmental factors as well as through normal use. Although mar and scratch are in many respects differing degrees of the same thing, a coating that improves mar resistance may not be effective in improving scratch resistance, and vice versa. It will be appreciated, therefore, that the present additive can be used in conjunction with other additives that impart improved mar and/or scratch resistance to coatings. For example, one additive that offers particularly good mar resistance can be coupled with one that offers particularly good scratch resistance.